NUTRITION IN POLYPI. ()7 



digestion of the food by the aid of the microscope. 

 Trembley watched this process with unwearied 

 perseverance for days together, and has given the 

 following account of his observations. The hydra, 

 though it does not pursue the animals on which it 

 feeds, yet devours with avidity all kinds of living- 

 prey that come within the reach of its tentacula, 

 and which it can overcome and introduce into its 

 mouth. The larvae of insects, naides, and other 

 aquatic worms, minute Crustacea, and even small 

 fishes are indiscriminately laid hold of, if they 

 happen but to touch any part of the long filaments 

 which the animal spreads out, in different direc- 

 tions, like a net, in search of food. The struggles 

 of the captive, which finds itself entangled in the 

 folds of these tentacula, are generally ineffectual ; 

 and the hydra, like the boa constrictor, contrives, 

 by enormously expanding its mouth, slowly to 

 draw into its cavity animals much larger than its 

 own body. Worms longer than itself are easily 

 swallowed by being previously doubled together 

 by the tentacula. Fig. 242 shows a hydra in the 

 act of devouring the vermiform larva of a Tipula, 

 which it has encircled with its tentacula, to which 

 it has applied its expanded mouth, and of which it 

 is absorbing the juice, before swallowing it. Fig. 

 243 shows the same animal after it has succeeded, 

 though not without a severe contest, in swallowing 

 a minnow, or other small fish, the form of M'hich is 

 still visible through the transparent sides of the 

 body, which are stretched to the utmost. It occa- 

 sionally happens, when two of these animals have 

 both seized the same object by its different ends, 

 that a struggle between them ensues, and that the 



